In the use of engines such as in work vehicles, starting, particularly in cold weather can be a problem. Where the engine has an associated clutch, starting can be facilitated by disengaging the clutch during start-up in order to reduce load on the engine. A clutch which is hydraulically actuated, for example, is actuated at a preset fluid pressure level supplied by a hydraulic pump usually driven by the engine itself. When the engine is shut-down, fluid can remain in the hydraulic circuit which keeps the clutch engaged or, during starting operations, turning over the engine will actuate the hydraulic pump which can supply fluid at a sufficient pressure level to engage the clutch and load the engine before the engine is fully engaged or during its warm-up period.
In some systems, it may not be possible to disengage the hydraulic pump before start-up because that pump is also used to supply other hydraulic systems, such as the drive bearings, associated with an engine driven pump. When this is the case, it is desirable to limit the maximum pressure level of hydraulic fluid from the pump to below that required for actuation of the clutch but maintain a sufficient level for other demands. It is also desirable to maintain this condition in the system for varying periods to allow for a sufficient warm-up period for the engine and to automatically disengage the clutch upon shut-down of the engine and without an external signal, such as by the operator, to prepare the engine or work vehicle for the next start-up.
The present invention is directed to overcoming one or more of the problems as set forth above.